Real-time modulation of visual feedback on human full-body movements in a virtual mirror: development and proof-of-concept

Abstract

BackgroundVirtual reality (VR) provides interactive multimodal sensory stimuli and biofeedback, and can be a powerful tool for physical and cognitive rehabilitation. However, existing systems have generally not implemented realistic full-body avatars and/or a scaling of visual movement feedback. We developed a “virtual mirror” that displays a realistic full-body avatar that responds to full-body movements in all movement planes in real-time, and that allows for the scaling of visual feedback on movements in real-time. The primary objective of this proof-of-concept study was to assess the ability of healthy subjects to detect scaled feedback on trunk flexion movements.MethodsThe “virtual mirror” was developed by integrating motion capture, virtual reality and projection systems. A protocol was developed to provide both augmented and reduced feedback on trunk flexion movements while sitting and standing. The task required reliance on both visual and proprioceptive feedback. The ability to detect scaled feedback was assessed in healthy subjects (n = 10) using a two-alternative forced choice paradigm. Additionally, immersion in the VR environment and task adherence (flexion angles, velocity, and fluency) were assessed.ResultsThe ability to detect scaled feedback could be modelled using a sigmoid curve with a high goodness of fit (R2 range 89-98%). The point of subjective equivalence was not significantly different from 0 (i.e. not shifted), indicating an unbiased perception. The just noticeable difference was 0.035 ± 0.007, indicating that subjects were able to discriminate different scaling levels consistently. VR immersion was reported to be good, despite some perceived delays between movements and VR projections. Movement kinematic analysis confirmed task adherence.ConclusionsThe new “virtual mirror” extends existing VR systems for motor and pain rehabilitation by enabling the use of realistic full-body avatars and scaled feedback. Proof-of-concept was demonstrated for the assessment of body perception during active movement in healthy controls. The next step will be to apply this system to assessment of body perception disturbances in patients with chronic pain.

Assessing the Perception of Trunk Movements in Military Personnel with Chronic Non-Specific Low Back Pain Using a Virtual Mirror

“…The project was performed in collaboration with the Canadian Armed Forces (CAF). A convenience sample of 16 military personnel with CNSLBP and 16 age-matched military HC subjects (aged between 18–55 years, men only to comply with the avatar’s gender) were recruited at a regional military base (sample size based on a proof-of-principle study including 10 healthy military subjects [ 29 ]). Subjects with CNSLBP were eligible when reporting persistent low back pain for at least 3 months, and when physically capable of performing repetitive trunk exercises.…”

“…Recently, we developed a “virtual mirror” displaying a realistic full-body avatar that responds to full-body movements in all movement planes in real-time [ 29 ]. This “virtual mirror” can be used to artificially exaggerate (i.e., augment) or reduce the visual feedback on actual movements at a specific joint, while providing normal feedback at other joints.…”

Exploring the Relationships Between Altered Body Perception, Limb Position Sense, and Limb Movement Sense in Complex Regional Pain Syndrome

“…The sense of limb movement was evaluated as described by Roosink et al 27,28 First, results obtained with the 2-alternative forced choice paradigm (greater = 1, smaller = 0) were plotted against the 13 scaling factors (log-transformed to be on a linear scale). Second, a sigmoid curve (1), with initial values X Y.50 = 0, constraints Y MAX = 1 and Y MIN = 0, and a variable slope (m), was fitted to the data using Prism 6 for Windows (GraphPad Software, La Jolla, CA):…”

Patterns of whole-body muscle activations following vertical perturbations during standing and walking

“…A motion capture system (Vicon, Oxford, UK) concurrently tracked the three-dimensional coordinates of 41 passive-re ective markers a xed to the body of each participant with a sampling rate of 120 Hz and spatial accuracy of 1 mm. The implemented marker setup followed Vicon's 'HumanRTKM' model [38]. The platform included two force plates and contained an embedded treadmill that operated in selfpaced mode, allowing participants to adjust treadmill speed to preferred walking speed [39].…”